<mat-toolbar color="primary">
  <div *ngIf="user">{{user.email}}</div>
  <button mat-button (click)="signIntoGithub()" *ngIf="!user">Sign In with Github</button>
  <button mat-button (click)="signOutFromGithub()" *ngIf="user">Sign out</button>
</mat-toolbar>

